False twist-crimped polyester yarns and process for their production

ABSTRACT

A false twist-crimped polyester yarn having a density d of 1.3800 &lt; OR = d &lt; OR = 1.3950 (g/cm3) and a total percentage crimp (TC) of TC &gt; OR = 30% is produced by false twisting a polyester multi-filament having a birefringence ( Delta n) of 0.030 &lt; OR = Delta n &lt; OR = 0.145 while heat setting the filament in the twisted state at 160* to 210* at a draft (dr) which satisfies the following equation:

United States Patent [191 Tkeda et a1.

[ FALSE TWIST-CRIMPED POLYESTER YARNS AND PROCESS FOR THEIR PRODUCTION [75] Inventors: Morio Ikeda; Mamoru Tsumoto,

both of Ibaraki, Japan [73] Assignee: Teijin Limited, Osaka, Japan [22] Filed: Apr. 5, 1971 [21] Appl. No.: 131,242

[30] Foreign Application Priority Data [451 Mar. 19, 1974 3,587,220 6/1971 Eggleston 57/140 3,601,972 8/1971 Rogers et al 57/157 FOREIGN PATENTS OR APPLICATIONS 746,992 3/1956 Great Britain 57/157 S Primary ExaminerWerner H. Schroeder Attorney, Agent, or Firm-Sherman and Shalloway [57] ABSTRACT A false twist-crimped polyester yarn having a density d of 1.3800 d 1.3950 (g/cm) and a total percentage crimp (TC) of TC 2 30% is produced by false twisting a polyester multi-filament having a birefringence (An) of 0.030 Art 5 0.145 while heat setting the filament in the twisted state at 160 to 210 at a draft (dr) which satisfies the following equation:

-250. An+38 d, g 150.An+ l7 Heat-setting the above false twist-crimped polyester yarn at a higher temperature gives a modified false twist-crimped polyester yarn having a density (d) of 1.3800 d 1.3950 (g/cm), a total percentage crimp (TC) of TC and a torque (Tq) of Tq 26 (T/ cm).

6 Claims, 6 Drawing Figures Apr. 6, 1970 Japan -29236 [52] US. Cl 57/140 R, 57/157 TS [51] Int. Cl D02g 1/02, D02g 3/02 [58] Field of Search 57/55.5, 140 R, 140 BY, 57/157 R, 157 S, 157 TS;264/103, 168, 210, 290

[56] References Cited UNITED STATES PATENTS 3,458,986 8/1969 Allison et al 57/140 2,980,492 4/1961 Jamieson et a1..... 57/157 8 3534.541 10/1970 Edison 57/157 TS [L 2 tr 0 E1 t. O k.-

OrL I l I G 5 45- 2 O 8 40- I x Lu 5 bl AT TEMPERATURE I I l I I60 I I I 200 OF YARN ('c) (ON THE HEATER) SHEET 1 [1F 5' Fig.1

TEMPERATURE O YARN (ON THE HEATER) PATENTEDHAR 19 I974 PATENTEU MR 1 9 I974 SHEET 2 BF 5 Fig.2

I I I 200 210 220 230 240 U AZPOP TEMPERATURE OF YARN (c) (ON THE HEATER) PATENTEU m 1 9 m4 SHEEI 3 BF 5 Fig.3

BIREFRINGENCE PATENIED m 1 9 m4 SHEET BF 5 BIREFRINGENCE nu) UNDRAWN YARN 1 FALSE TWlST-CRIMPED POLYESTER YARNS AND PROCESS FOR THEIR PRODUCTION This invention relates to a false twist-crimped polyester yarn or modified false twist-crimped polyester yarn having both highly improved crimp elongation hereinafter refered to as total percentage crimp and highly improved dyeability, characteristic which the conventional false twist-crimped polyester yarns cannot possess at the same time, and to a process for producing such yarns.

More particularly, the invention relates to a false twist-crimped polyester yarn having a density d of 1.3800 d 1.3950 (g/cm) and a total percentage crimp (TC) of TC 3O and to a modified false twist-crimped polyester yarn having a density d of 1.3800 d 5 1.3950 (g/cm"), a total percentage crimp (TC) ofTC 20 and a torque (Tq) of Tq 26 (T/25 cm), such modified false twist-crimped polyester yarn being obtained by subjecting the firstmentioned polyester yarn to a second heat set treatment.

The false twist-crimped polyester yarn of the invention has a density d of the above specified range which the conventional flase twist-crimped polyester yarn cannot have for a TC of the above range (the conventional crimped yarn has a density of about 1.398 d 1.410). The modified false twist-crimped polyester yarn of the invention has a density different from that of the conventional polyester yarn for the specified TC, and also a torque which the conventional polyester yarn cannot have for the specified TC (the conventional polyester yarn has a torque of more than about 30).

The invention also provides a process for producing a false twist-crimped polyester yarn which comprises false twisting a polyester multifilament having a birefringence (An) of 0.030 An 0.145 preferably' 0.06 An 0.135 while heat-setting such multifila ment in the twisted state at 160 to 210C., preferably 170 to 200C. at a draft d, expressed by the equation 25O-An+38 d, ;l50'An+17....(I);and to a process for producing a modified false twistcrimped polyester yarn which comprises subjecting the false twist-crimped yarn so obtained to a second heatsetting at a temperature in excess of that at which the yarn has been initially heat set, by any means known per se.

The polyester yarns having novel improved properties can be produced by the processes of the invention on the basis of the two important findings that the birefringence (An) of the starting polyester multifilament has not previously been employed (previously up to about 0.16 at the lowest) and that the draft is chosen correspondingly to the varying An of the starting yarn.

Polyester filament yarns, especially polyethylene terephthalate filament yarns, have high tenacity and Youngs modulus, and therefore have found wide applications as apparel, interior decoration and industrial materials. For apparel uses, it is general practice to produce woven or knitted goods by using crimped polyester filament yarns, or blend yarns obtained by mixing slightly crimped filament yarns cut to staple lengths with cotton, wool, or the like. In recent years, the use of crimped filamentary yarns, especially the use of false twist-crimped filamentary yarns, has attracted special attention.

The false twist crimping process is performed continuously by using a false twist by which a filament yarn is heat set in a state of being twisted in one direction, and then untwisted in a direction reverse to the twist direction. The crimp is obtained by heat-setting the filament yarn in the twisted state thereby leaving the torsion permanently in the form of a twist. Therefore, whether the false twist-crimped yarn obtained by such a method has excellent crimp properties is determined by whether the filament yarn has been fully heat set in the twisted state.

Polyester filament yarns now in use for false twist crimping have high Youngs modulus and melting point higher than other synthetic filaments such as polyamide filaments, and therefore, it is extremely difficult to leave a molecular torsion in the form of twist in the filament yarn. In order to obtain sufficient crimping effects, the heat setting of the filament yarn should be as high as 210 to 230C.

Such high temperatures are useful for obtaining good crimps. But the requirement for great quantities of heat energy inevitably results in the deterioration of fiber properties during processing and in the non-uniformity of quality. Furthermore, commercially available false twist crimped yarns of polyesters do not possess entirely satisfactory properties. They have low dyeability (dye exhaustion of less than percent with disperse dyes), and there is a frequent occurrence of the nonuniformity of dyeing within and between spindles during crimping. It must be especially noted that attempts to provide yarns of satisfactory total percentage crimps inevitably result in reduced dyeability, and the extent of reduction changes greatly with slight changes in the heat-setting temperature.

The low dyeability means poor utilization of dyestuffs, Because of the non-uniformity of dyeing, it is now necessary to cut the false twist-crimped yarn obtained in each spindle to certain lengths, measure the dyeability of each yarn, and sort out the yarns according to dyeability prior to use. This is course requires extra labor, and even such treatment cannot obviate a great loss owing to the products of poor quality.

Accordingly, an object of the present invention is to provide a false twist-crimped polyester yarn which has the same or better crimp properties, especially total percentage crimp (TC), as compared with the conventional false twist-crimped polyester yarns, and which has a dyeability (dye exhaustion) and level dyeing property previously incapable of being attained for the TC range specified in the present invention, and also a modified false twist-crimped polyester yarn obtained by subjecting the 'false twist-crimped polyester yarn to a second heat setting.

Another object of the invention is to provide a process for producing such false twist-crimped polyester yarn having such novel improved properties and the modified false twist-crimped polyester yarn obtained therefrom.

Still another object of the invention is to provide a process for producing a false twist-crimped polyester yarn having dyeability and level dyeing property, which has a total percentage crimp comparable to that of the conventional false twist-crimped polyester yarns even when processed at temperatures lower than the conventional false twisting temperatures.

Many other objects and advantages of the present invention will become apparent from the following description.

As a result of strenuous study for achieving the above objects, the following has been found. Severe high temperature conditions of 210 to 230C. are necessary. In fact such temperature is employed for obtaining polyester fibers having the percentage crimps required in the market. It has been found that if polyester filaments of lower birefringence (An) are used, false twistcrimped yarns having substantially the same percentage crimps as the conventional filaments can be obtained by false twisting the filaments while drafting at a temperature of less than 210C., especially about 190C. It has however been found that in spite of the satisfactory percentage crimps of such false twistcrimped yarns, dyeings of woven or knitted goods made of these crimped yarns have a number of striped spots which make the final products still unsatisfactory. In finding out the cause of this, it has been ascertained that the birefringence of polyester filament yarns is closely related to the tension of the yarns at the time of the false twisting treatment, and this has led to the accomplishment of the present invention.

Specifically, when polyester filaments having a birefringence of 0.030 to 0.145 are false twist-crimped at a draft specified by the Equation I above, satisfactory crimping becomes possible at lower temperatures in the range of 210C. to 160C, and various difficulties which reduce the value of the final products, such as the occurrence of striped spots, non-levelling, or poor dyeability, can be overcome.

The birefringence (An), total percentage crimp (TC) and dye exhaustion (L-value) are defined as follows:

A. Birefringence (An) Sodium D rays (wavelength 589 millimicrons) are used as a light source, and the specimen filaments are disposed in a diagonal position. The birefringence (An) of the specimen is computed from the following equation:

where n is the interference fringe due to the degree of orientation of the polymer molecular chain: r is the retardation obtained by measuring the orientation not developing into the interference fringe by means of a Bereks compensator; a is the diameter of the filament; and A is the wavelength of the sodium D rays.

B. Total Percentage Crimp (TC) A yarn processed on a false twist crimper is placed under an initial load of 2 mg/de and a heavier load of 0.2 g/de. After a lapse of 1 minute, the length (1 is read. Immediately the heavier load is removed, and the yarn under the initial load is placed in boiling water. It is taken out of the water minutes later. The initial load is removed, and the yarn is naturally dried for 24 hours. The initial load and the heavier load are again exerted on the dried yarn, and its length (1 is read after a lapse of 1 minute. Immediately, the heavier load is removed, and after a lapse of 1 minute, its length (1 is read. The total percentage crimp (TC), which is the crimp properties of the false twisted filaments, is expressed by the following equation:

"rc (1 l3)/l,, x

C. Dye exhaustion (L value) A yarn processed by a false twist crimper is circular knitted. The knitted article is dyed for 30 minutes in boiling water using a dye bath containing 3 4% of Eastmann Polyester Blue BLF and 0.5 g/liter of Monogen at a goods-to-liquor ratio of 1:100. The lightness (Is-value) of the dyeing is measured by a CM-20 type color differentlal meter fl ip p on Color Machine Company. This L-values is employed as the dye exhaustion. LargerL-value mean lighter colors, and smaller L-values mean darker colors.

To facilitate the understanding of the invention, reference may be made to the accompanying drawings in which:

FIG. 1 is a schematic representation of the reaction between the heat treating temperature and the time required to attain the secondary crystallization:

FIG. 2 is a graphic representation showing one example of the relation among the false twist crimping temperature of the polyester filament (temperature of the filament), the dye exhaustion (L-value) and the total percentage crimp of the filament;

FIG. 3 is a graphic representation showing the relation between the birefringence of the starting polyester filaments of the invention and the draft employed in the false twist crimping treatment;

FIG. 4 is a schematic arrangement of one example of a false twisting apparatus suitable for the production of the false twist-crimped polyester yarns of the present invention;

FIG. 5 is a graphic representation showing the relation between the birefringence of an undrawn polyester filament and the draw ratio; and

FIG. 6 is a view showing one example of a drawing apparatus suitable for drawing by a dry heat drawing method in order to obtain a polyester filament having a birefringence 0.030 An 5 0.145.

Referring to FIG. 1, the axis of abscissas represents the temperature of the filament on the heater, and the axis of ordinates, the time required until the secondary crystallization is attained. The curve a shows the conventional polyester filament, and the curve b, the starting polyester filament of the present invention. The denier size (de/fil), birefringence (An), and draft of the filament used are as follows:

By the term time required until the secondary crystallization is attained," used herein, is meant the time of the initial stage where a substantially straight line relation is established between the logarithm of the time required to treat the specimen at a certain temperature and the density of the specimen. The t in the ordinate shows the time required for obtaining good crimps. When the time is shorter than t the desired heat treating time cannot be attained, and the treating time longer than means that on the lower temperature side, heat setting is insufficient, and on the higher temperature side, the melt-adhesion of the filaments occur. Thus, in order to obtain good crimp setting effects, the time required until the secondary crystallization is attained should be within the range of r, to

t that is to say, the secondary crystallization should not precede the setting of the yarn form. Now referring to the drawing from this point of view, it is found that with the conventional polyester filament, at a temperature below T the secondary crystallization is reached before arriving at the heat-treating time t, t and therefore, good crimp setting effects cannot be obtained. For instance, at about 180C, the secondary crystallization stage is reached almost instantaneously, and the time is less than seconds. At higher temperatures, the time required to attain the secondary crystallization stage becomes longer. Therefore, in order to obtain the treating time t, t within the range where the secondary crystallization does not precede, the processing is compelled to be performed at a temperature in the range of T to T As T T the temperatures of 210 to 230C. are generally used.

With the polyester filament of the present invention, the temperature corresponding to the minimum time required to attain the secondary crystallization exists within the range of T to T and this time becomes gradually longer both on the lower temperature side and the higher temperature side. It is assumed that the filaments showing such behavior of crystallization may have a different crystalline structure from that of the conventional polyester filaments. Such behavior of crystallization leads to ease of processing. Within the time range of l, to for obtaining good crimp setting effects, the temperatures in the range of T to T can be employed for the false twist crimping treatment. Such lower temperatures could not be used previously for false twist crimping of polyester filaments.

The dye exhaustion of the processed yarn of the in- I vention is shown in FIG. 2 by the curve b,. It is seen from the curve b, that at temperatures below 210C., the dyeing difference (AD) in relation to the temperature difference (AT) is very small, and the dye exhaustion is markedly improved over the conventional false twist-crimped polyester yarns.

On the other hand, with the conventional false twistcrimped polyester yarns, the dyeing difference (AD) with the temperature difference (AT) is very large as shown by the curve a, of FIG. 2. If a number of such yarns having the temperature non-uniformity are used to produce woven or knitted articles, the resulting articles present clear dyeing non-uniformity, and are not suitable for sale on the market.

The curves a and h of FIG. 2 represent the total percentage crimps of the crimped yarns corresponding to a and b,. The total percentage crimp of the crimped polyester yarn of the invention becomes maximum at a temperature in the range of 160 to 210C. within which excellent level dyeing properties and dyeability can be obtained. In contrast, with the conventional false twist-crimped polyester yarns, the total percentage crimps become maximum at 210 to 230C. and above. It is seen from FIG. 2 that the conventional crimped polyester yarns have the desired total percentage crimps only when heat set at a temperature above 210C., and suffer from considerably large fluctuations in dyeing difference (AD) with the temperature difference (AT) and also reduced dye exhaustion; whereas the present invention provides crimped yarns having 6 comparable total percentage crimps and good dyeability and level dyeing properties by processing at lower temperatures of to 210C. It is appreciated that the processing temperatures in the range of to 200C. are especially preferred for obtaining good dyeability and level dyeing properties.

FIG. 3 shows that when the birefringence of the filament is set, the draft should be confined within a certain range. When polyester filament yarns having the birefringence specified in the invention are processed at a draft shown by the area A, in the drawing, the twisting tension becomes very small, and there is frequent occurrence of non-untwisted yarns or meltadhered yams. This makes it impossible to obtain crimped yarns which serve for practical purposes. When the yarns are processed at a draft shown by the area A in the drawing, the twisting tension becomes very great, and the non-untwisted yarns or meltadhered yarns do not occur to such an extent, but the crimp characteristics of the yarns become poor. Therefore, crimped yarns of practical value cannot be obtained. Accordingly, the draft specified in the invention is necessary for maintaining the yarn tension during twisting within the range of 0.05 to 0.15 g/de which has been required in the conventional false twisting in order to obtain stable twisting effects.

If the draft is in the area shown by A in the drawing, the yarn exhibits the same properties as an undrawn yarn, and it is impossible to obtain crimped yarns of practical value. In the area A the crimp characteristics, dye exhaustion, and level dyeing property are hardly improved. It is appreciated therefore that when polyester filaments having a birefringence of 0.06 E An 0.135, preferably 0.06 An 0.120 are used, crimped yarns can be obtained which are most satisfactory in crimp characteristics, dye exhaustion and level dyeing property. The area formed by connecting h, i. j and k with one another in FIG. 3 satisfies the requirements for obtaiiiing the crimped yarns of the invention, and the area formed by connecting l, m, n and o with one another is the preferred range. It is absolutely necessary therefore that the draft at the time of false twisting should be prescribed in relation to the birefringence of the polyester filaments used.

Referring to FIG. 4, polyester filament yarn 2 wound on pirn 1 passes snail guide 3 and is delivered by a pair of feed rollers 4 and 4. It then passes heater 5 and false twist spindle 6, and is then taken up by a pair of delivery rollers 7 and 7'. It is then wound up on bobbin 9 which rotates frictionally by roller 8. In this instance, the birefringence of the polyester filament yarn wound up on the pirn l is 0.030 to 0.145. It is necessary that such a filament yarn should be processed between the feed rollers 4 and 4' and the delivery rollers 7 and 7' under the draft which satisfy the foregoing Equation l. Generally draft (dr) is determined by the following equation.

draft (dr) (V V1)/V X 100 wherein V, stands for the peripheral speed of the feed roller 4, 4' and V for the peripheral speed of delivery roller 7, 7.

The type of the false twist crimping is not particularly restricted, but the spindle method is especially preferred. If desired, a secondary heater may be provided between the spindle 6 and the delivery rollers 7 and 7 in order to heat-treat the crimped yarn and reduce the torque of the yarn.

In FIG. 6, the numeral 10 shows a cheese, 11 an undrawn polyester yarn, 12 a roller for exerting a preliminary tension, 13 a hot feed roller, 14 a draw roller, 15 a guide and 16 a drawn yarn. In the drawing of an undrawn polyester yarn using this apparatus, it is preferable to impart a preliminary tension to the yarn to an extent such that the undrawn yarn will not substantially be drawn between the roller 12 and the hot roller 13. This can desirably be done by controlling the peripheral speed ratio between the roller 12 and the hot roller 13. The proper ratio of peripheral speed between the roller 12 and the hot roller 13 is about 1: 1001-1030. A heat-treating device such as a slit heater or hot plate may be provided between the hot roller and the draw roller in order to heat set the drawn yarn.

The starting polyester filament yarn to be false twistcrimped by the process of the invention can be obtained by drawing an ordinary undrawn polyester yarn at a low draw ratio in dry heat using a heated feed roller, heated drawing pin or plate or wet heat (including warm water bath). For obtaining polyester yarns having a birefringence of 0.030 to 0.145, it is necessary to employ a suitable draw ratio (Dr) according to the birefringence (Am) of the undrawn yarn. The following relation has been found to exist between Dr and An i. when 0.002 An 0.0l0l00'An+2.50 Dr E -120An 4.00 L! ii. when 0010 An 0.020 -25-An 1.75

In FIG. 5, the range which satisfies the above relations is shown by the hatched area. If the draw ratios which satisfy the above Equations II and III are used according to the birefringence of the undrawn yarn, the drawn polyester filaments can have a birefringence of 0.030 to 0.145.

As regards the wet heat drawing, the desired polyester filaments can be obtained by maintaining the drawing tension at 0.01 to 1.00 g/de in a water bath at 80 to l00C. The drawing under these specified conditions leads to the formation of filament yarns which are molecularly oriented uniformly and free from necking. It is therefore necessary to adjust the drawing tension to a range of 0.01 to 1.00 g/de. If the drawing tension is less than 0.01 g/de, substantial molecular orientation does not occur, and the drawn yarn has much the samephysical properties as an undrawn yarn. On the other hand, when the drawing tension exceeds 1.00 g/de, a high degree of molecular orientation occurs in the filament, and the properties become the same as those of the conventional polyester filaments. The drawing tension varies depending upon such factors as the type of the undrawn yarn, the temperature of the draw bath, the draw ratio, or the draw speed. In the case ofa 155 denier/24 filaments undrawn polyester yarn having a birefringence of 0.0105 and an intrinsic viscosity of 0.59, the drawing tension will become 0.01 1.00 g/de when the yarn is drawn at a draw ratio of 1.40 to 2.80 at a draw bath temperature of about 90C. and at a feed rate of 300 meters per minute.

Other methods of drawing are also available. For instance, an undrawn filament yarn extruded from a spinning nozzle is drawn between two pairs of rollers without prior wind-up, or an undrawn filament extruded from a spinning nozzle is first wound up on a bobbin rotating at peripheral speed of 3,000 meters per minute, and molecular orientation is induced in the meantime to form filaments having the desired birefringence.

The differences between the present invention and the prior art (British Pat. No. 777,625, British Pat. No. 746,992) will be discussed below at some length.

British Pat. No. 777,625 discloses that an undrawn yarn is drawn to more than several times the original length and simultaneously false twist-crimped. In this process, a tension as high as at least 0.2 g/de is exerted on the yarn, although it depends on the physical properties of the yarn, and under such a high tension, the twisting effect on the yarn is hardly obtainable. Therefore, this process can give a drawn yarn, but not a crimped yarn of practical value. Furthermore, in the process wherein drawing and false twist crimping are simultaneously performed, there will be a greater nonuniformity of dyeing if the processing is done under such conditions as to give good crimped yarns; thus, it is impossible to obtain serviceable crimped yarns by the process disclosed in this British Patent.

British Pat. No. 746,992 discloses the imparting of a draft of 0.5 to 20 percent at the time of false twisting. The starting raw yarn to be processed is a completely oriented or highly oriented drawn yarn (birefringence of greater than 0.160) of Terylene or Dacron. The drafting performed in the British Patent is intended to obtain twist yarns having uniform twist effect and to prevent duplicating twists, etc., when the yarn is false twist crimped in an overfeed state in a conventional manner. The undrawn polyester yarns used in the present invention are a substantially non-oriented polyester filament consisting of a polyester containing at least percent of ethylene terephthalate units. The preferred polyester is polyethylene terephthalate, but copolyesters containing less 'than 20 percent of other copolymerizable components may also be used. Examples of other acid components to be copolymerized with ethylene terephthalate include dibasic acids such as phthalic acid, isophthalic acid, adipic acid, oxalic acid, sebacis acid, suberic acid, glutaric acid, pimelic acid, fumaric acid, or succinic acid. Examples of other alcohol components that can be copolymerized with ethylene terephthalate are dihydric alcohols such as polymethylene glycols having two to 10 carbon atoms (trimethylene glycol and butylene glycol, for example), cyclohexane dimethanol, etc.

The polyester may contain a minor amount of a modifier such as 5-oxydimethyl isophthalate, 5-oxydimethyl hexahydroisophthalate, benzene-l ,3,5-tricarboxylic acids, para-carbomethoxyphenyl diethyl phosphonate, 3,5-dicarboxy phenyl diethyl phosphate, pentaerythritol, glycol, phosphoric acid, triphenyl phosphate, tri-l-carbomethoxyphenyl phosphate, triphenyl arsenite, tricapryl boric acid, sorbitan, trimesic acid, or diethylene glycol. Furthermore, the polyester may contain a small amount of another polymer such as a polyamide, polycarbonate, or polyolefin.

The undrawn polyester yarns used in the present invention may be those obtained by melt-spinning the aforementioned-polyesters. Especially preferred are those having a denier size of not more than denier per monofilament, a birefringence of 0.002 to 0.020, and an intrinsic viscosity of 0.3 1.2, as computed from the value measured in o-chlorophenol at 35C. The drawing of an undrawn yarn composed of a polyester having an intrinsic viscosity of less than 0.5 presents difficulties in operation such as the occurrence of fuzzes in an ordinary hot pin drawing procedure. in such a case, the undrawn yarn of a polyester of low detained by subjecting the aforementioned false twista torque ofnot more than 26 (T/25 cm).

The torque and the density used in the invention are gree of polymerization can be satisfactorily drawn by determined as follows: using the hot roller drawing procedure. D. Torque The undrawn yarn may not only have a circular sec- The specimen false twist-crimped yarn is set at both tion, but also a n0n-circular section such as triangle, ends spaced from each other at a distance of about 1 quadangle, pentagonal, flat, or cruciform section and a m, and a load of about 1 mg/de is applied to the central hollow section such as doughnut or non-circular hollow p t O the yarn. The yarn is bent at the point of the ti load. The yarn is fixed at a point at which the intertwin- Thus according to the present invention, a low torque g g n r 38 a sul 0f t ending is maxifalse twist-crimped ol te am f hi hl im d mum. The torque is expressed by the number of twists dyeability can be obtained by dexterously combining Present P r 25 cm f th yarn for unthe birefringence of the polyester filaments, the conditwisting- A crimped y having a larger number of tions for drawing the filaments, the draft at the time of twists has a larger q The torque Values described false twist crimping procedure which is dependent on in the present application are the averages of the meathe birefringence, and the processing temperatures. Sllfed Values of P The crimping operation can be performed at lower Densityi temperatures than in the conventional methods, and 20 The p m is P into a nsi y gr i nt tub f the resulting crimped yarns have comparable percentn-heptane-cafbofl tetrachloride using a float age crimp, and good dye exhaustion which hardly fluc- (Precision 2 X g/ m (made y Shi ayama tuates even with the false twisting temperatures. The emific Instruments Works, The density is advantage of the present invention resides in the fact 25 Sured after a p of 48 hours h d f l t i p i d yams can b b i d The invention will further be described by the followeven when the false twisting temperature is below ing Examples- 200C. The invention also has the advantage that at this I 7' 7 '7 V temperature, there is hardly any change in the differ- EXAMPLE 1 ence of dye exhaustion, and no inspection is necessary Polyethylene terephthalate chips having an intrinsic to sort out the yarns according to the difference of dye viscosity of 0.65 were melted at 288C, and extruded exhaustion. That the false twisting temperature can be through a spinneret having 24 orifices, each having a maintained at a low level helps to increase the speed of diameter of 0.25 mm, followed by windingup as untwisting to a marked extent, and this has a great indusdrawn filaments. The intrinsic viscosity of the undrawn trial significance. The length of the heater of the false filaments was 0.63, and they had a birefringence of twister and the size (especially height) of the machine 1050 X 10 The drawing conditions of the undrawn are naturally restricted, and with increasing processing filaments, the properties of the drawn filaments, and temperatures, the speed of processing must be reduced the conditions under which the drawn filaments were in order to obtain the desired heat-treatment effects. fa se ist-crimped by using a false twisting crimping However, when the false twisting can be performed at ehi e Of e type shown in FIG. 4 are shown in Table lower temperatures 151 t ptsisqii s tiqm.Phase Table 1 Sample A B C D Drawing heating means warm water hot roller hot roller warm water conditions temperature (C) 95 85 draw ratio (x) 1.80 2.73 2.73 1.80 draw speed (m/min) 600 1000 1000 600 Physical denier size (de/fil.) 944/24 78.8/24 76.4/24 88.9/24 properties birefringence (An) 0.045 0.138 0.138 0.045 of the tenacity at break (g/de) 3.2 3.8 3.8 3.2 drawn yarn elongation at break 45 45 135 density (g/cm) 1.350 1.365 1.365 1.350

Flase twist number of false twists (TIM) 3380 3380 3380 3380 crimping draft 21 l -2 14 conditions processing speed (m/min) I00 100 I00 100 twist tension at C. (gr/dc) sired heat-treating effects can be obtained within shorter periods of time, and therefore higher speeds of processing.

The false twist-crimped polyester yarns of the invention have a density of 1.3800 5 d 1.3950 (g/cm) which the conventional yarns having a total percentage crimp of not less than 30 percent cannot possess, and this contributes to the marked improvement of dyeing properties.

The modified false twist-crimped polyester yarns ob- Ten spindles were used for the crimping of the drawn filaments. The temperatures were varied from spindle to spindle by a maximum of i 4C. based on the standard spindle. Thus, ten false twist-crimped yarns were obtained. The total percentage crimps (TC) of these 7 crimped yarns and their dyeing characteristics are shown in Table 2. It is seen from the Tables that according to the present invention, even if the temperature non-uniformity among the spindles exists, the crimp non-uniformity of the yarns does not occur, and

the dye exhaustion difference (D maximum dye exhaustion minimum dye exhaustion) is negligibly small at temperatures at which the total percentage crimps of the yarns are large.

Ten spindles were used for crimping of drawn yarns, and the temperatures were varied from spindle to spindle by a maximum of: 4C. based on the standard spinthe spindles, the crimp non-uniformity of the yarns Table 2 Total percentage crimp Dyeing properties Density of Processing Standard Crimp Standard Dyeing standard temperature spindle difference spindle difference spindle (C.) Sample (TCs) (ATC) (Ds) (AD) (g/cm) 170 B 32.6 S 5.0 37.8 S 0.4 1.3874 C 33.4 5.0 37.5 S 0.4 1.3876

A 43.1 S 4.0 35.3 i 0.2 1.3899

180 B 38.4 $4.0 37.9 S 0.2 1.3897 C 39.0 S 4.0 37.5 0.2 13896 190 B 40.7 $4.0 37.9 0.2 1.3919 C 41.5 $4.0 37.6 s 0.2 1.3921

A 45.1 s 2.0 35.2 s 0.8 1.3945

10 B 44.3 s 2.0 37.0 S 1.5 1.3963 C 44.6 2.0 36.9 5 1.5 1.3964

D 43.0 S 3.0 34.9 S 1.5 1.3965

EXKMPTQE 2 7 does not occur, and the dye exhaustion difference is The conditions for the drawing of undrawn filaments obtained in Example 1, the properties of the resulting drawn filaments, and the conditions for false twist' crimping of the drawn filaments using a false twisting crimping apparatus of the type shown in FIG. 4 are given in Table 3.

still small at temperatures at which the total percentage crimps of the yarns are large.

dle. Ten false twist-crimped yarns were obtained. The total percentage crimp and dyeing characteristics are given in Table 4. It is seen from the results shown in the above table that according to the present invention, even if the temperature non-uniformity exists among Table 3 Sample E F G H D wi heatin means warm water hot roller hot roller warm water conditions temperature (C.) 95 85 85 95 draw ratio (1) 210 2.54 2.54 2.10 draw speed (m/min) 600 1000 1000 600 Physical denier size (de/fll.) 90.5/24 82.7/24 79.6/24 85.8/24 properties birefringence (An) 0.078 0.1 0.115 0.078 of the tenacity at break (g/de) 3.4 3.7 3.7 3.4 drawn yarn elongation at break 92 6O 92 density (g/cm 1.354 1.362 1.362 1.354

False twist number of false twists (T/M) 3380 3380 3380 3380 crimping draft 16 6 2 10 conditions processing speed (m/min) 100 100 100 twist tension at 190C. (gr/dc) 0.110 0.102 0.087 0.093

Table 4' w W mm Total percentage crimp Dyeing properties Density of Processing Standard Crimp Standard Dyeing standard temperature spindle difference spindle difference spindle (C.) Sample (TCs) (ATC) (Ds) (AD) (g/ E 37.4 s 5.0 36.5 0.4 1.3873 F 35.6 E 5.0 36.9 S 0.4 1.3875 G 36.8 s 5.0 36.8 S 0.4 1.3875 H 38.1 5.0 35.7 0.4 1.3874

E 44.8 s 4.0 36.8 S 0.2 1.3900 180 F 43.7 4.0 37.2 0.2 1.3898 G 44.2 s 4.0 36.9 S 0.2 1.3897 H 44.6 4.0 36.1 0.2 1.3899

E 45.1 2.0 36.8 0.2 1.3917 F 44.5 s 4.0 37.1 5 0.2 1.3820

Table 4 :QQmLtued Total percentage crimp Dyeing properties Density of Processing Standard Crimp Standard Dyeing standard temperature spindle difference spindle difference spindle (C.) Sample (TCs) (ATC) (Ds) (AD) (g/cm) 6 45.4. S4.0 36.8 S 2.0 1.3822 H 46.0 S 2.0 36.0 s 0.2 1.3819

E' 45.2 S 2.0 36.7 S 0.8 1.3942 200 F 44.8 S 2.0 37.1 S 0.8 1.3945 G 45.2 S 2.0 36.7 S 0.8 1.3944 H 46.3 S 2.0 35.8 s 0.8 1.3943

E 42.8 s 3.6 36.1 s 1.5 1.3964 210 F 44.4 S2.0 36.2 S 1.5 1.3962 G 44.7 S 2.0 35.9 S 1.5 1.3968 H s 3.0 34.0 S 1.5

COMPARATIVE EXAMPLE 1 The conditions for drawing the undrawn yarn obtained in Example 1, the properties of the drawn yarns,

and the conditions for false twist crimping of the drawn yarns using a false twist-crimping apparatus shown in FlG. 4 are given in Table 5.

ties of these crimped yarns are shown in Table 6. 1t is seen from Table 6 that in Samples M and 0, nonuntwisted yarns and melt-adhered yarns occurred and it was impossible to obtain crimped yarns of practical values, and that in Samples I and K in which a twisting tension was large, the crimp properties of the yarns are Table 5 Sample 1 K M 0 Drawing heating means warm water hot roller hot roller warm water conditions temperature (C) 95 85 draw ratio (x) 1.80 2.73 2.73 1.80

draw speed (m/min) 600 1000 1000 600 Physical denier size (de/fil.) /24 858/24 73.6/24 81.9/24 properties birefringence (An) 0.045 0.138 0.138 0.045 of the tenacity at break (g/de) 3.2 3.8 3.8 3.2 drawn yarn elongation at break 45 45 135 density (g/cm) 1.350 1.365 1.365 1.350

False twist number of false twists (T/M) 3380 3380 3380 3380 crimping draft 35 10 -6 5 conditions processing speed (m/min) 100 100 100 100 twist tension at 190C. (gr/dc) Ten spindles were used for the crimping of the drawn yarns. The temperatures were varied from spindle to spindle by maximum of i 4C. based on the standard spindle. Thus, ten false twist-crimped yarns were ob-.

poor, on the other hand considerably large difference (AD) of the dye exhaustion at processing temperatures at which the total percentage crimp is relatively large,

which in turn produces the tendency of the dyeing nontained. The total percentage crimps and dyeingproper: 45 uniformity among the spindles.

Table 6 Total percentage crimp Dyeing properties Density of Processing Standard Crimp Standard Dyeing standard temperature spindle difference spindle difference spindle )C.) Sample (TCs) (ATC) (D5) (AD) (g/cm) I 23.5 S 5.0 43.6 S 0.5 1.3872 K 14.3 S 5.0 45.7 S 0.5 1.3874

M (occurence of non-untwisted yarns) O (occurrence of non-untwisted yarns and melt-adhered yams) 1 28.7 S 3.0 45.1 S 0.3 1.3920 K 20.2 S 3.0 46.8 S 0.3 1.3918

M (occurence of non-untwisted yarns) O (occurence of non-untwisted yarns and melt-adhered yarns) 1 33.4 S 2.0 44.2 S 1.5 1.3963 210 K 28.5 S 2.0 45.6 S 1.5 1.3964

M (occurrence of non-untwisted yarns and melt-adhered yarns) C (occurrence of non-untwisted yarns and melt-adhered yarns) 1 31.6 S2.0 41.6 $2.5 1.3993 220 K 34.6 S20 42.1 62.5 1.3990

M (occurrence of non-untwiutcti yumn 11nd melt-adhered yurnn) O (occurrence of nun-untwiiucd yarns and melt-adhered yarns) 1 27.5 S50 37.8 s 5.0 1.4009 230 K 29.6 S 5.0 38.2 S 5.0 1.4007

M (occurrence of non-untwisted yarns and melt-adhered yarns) (occurrence of non-untwisted yarns and melt-adhered yarns) COMPARATIVE EXAMPLE 2 The conditions for drawing the undrawn yarns obtained in Example 1, the properties of the resulting drawn yarns, and the conditions for twist crimping of In Samples L and N in which the birefringence of the drawn yarn is large as in the conventional drawn yarns that are commercially available, the yarns have good total percentage crimps at the processing temperatures the drawn yarnsusing a false twist crimping machine of 5 above 210C But in this temperature range, the dye the type Show 4 are shown m Table exhaustion difference becomes maximum, and the Table 7 Sample J L N P Drawing heating means warm water hot roller hot roller warm water conditions temperature (C) 82 82 95 draw ratio (r) 1.40 3.04 3.04 1.40

drawspeed (m/min 200 1000 1000 200 Physical denier size (de/fil) 101.24 81.1/24 75.0/24 89.7/24 properties birefringence (An) 0.021 0.168 0.168 0.021 of the tenacity at 3.0 5.1 5.1 3.0 break (g/de) drawn yarn elongation at break 28 28 160 density (g/cm) 1.348 1.380 1.380 1.348

False twist number of false twists (T/M) 3380 3380 3380 3380 crimping draft 30 4 -4 5 conditions processing speed (m/min) 100 100 100 100 twist tension at 190C. (gr/dc) 0.084 0.385

dyeing non-uniformity tends to occur among the spindles.

EXAMPLE 3 Polyethylene terephthalate chips having an intrinsic viscosity of 0.65 were melted at 288C, extruded through a spinneret having 30 orifices, each having a diameter of 0.25 mm, and woundup as undrawn yarns. The undrawn yarns had an intrinsic viscosity of 0.62 and a birefringence of 560 X 10 The conditions for drawing these undrawn yarns, theproperties of the re- Table 8 Total percentage crimp Dyeing properties Density of Processing Standard Crimp Standard Dyeing standard temperature spindle difference spindle difference spindle (C.) Sample (TCs) (A TC) (Ds) (A D) (g/cm) .1 (occurrence of non-untwisted yarns and melt-adhered yarns) L s 8 45.2 s 0.5 1.3873 N 21.3 5 8 43.6 0.5 1.3872 P (occurrence of non-untwisted yarns and melt-adhered yarns) .I (occurrence of non-untwisted yarns and melt-adhered yarns) L 21.4 $8 46.4 $0.3 1.3919 N 28.6 s 5 44.0 S 0.3 1.3921 P (occurrence of non-untwisted yarns and melt-adhered yarns) J (occurrence of non-untvvisted yarns and melt-adhered yarns) 210 L 32.6 s 3 44.3 S 1 1.3963 N 36.4 s 5 42.2 s 1.5 1.3964 P (occurrence of non-untwisted yarns and melt-adhered yarns) J H (occurrence of non-untwiste d yarns and melt-adhered ya n s) 220 L s 3 41.5 s 2.5 1.3994 N 42.7 5 3 39.5 2.5 1.3991 P (occurrence of non-untwisted yarns and melt-adhered yarns) J (occurrence of non-untwisted yarns and melt-adhered yarns) 230 L s 5 37.5 s 5.0 1.4006 N 44.9 5 35.9 s 5.0 1.4005 P (occurrence of non-untwisted yarns and melt-adhered yarns) sulting drawn yarns, and the conditions for false twist crimping of the drawn yarns using a false twist crimping machine of the type shown in FIG. 4 in which second heat-treatiiigdevices are arranged at 7, 7' and 8 crimped yarns have little crimp non-uniformity, and small dyeing differences and torque at the temperatures at which the total percentage crimps are large.

are shown in Table 9. CbMFX1i AT1VE EXK1WFLE3 7' Ten spindles were used for crimping of the drawn I g v yarns, and the processing temperatures were varied Th di i f d i h undrawn yams from spindle to spindle by a maximum of i 4C. based tained in Example 3, the properties of the resulting on the standard spindle. The total percentage crimps, drawn yarns, and the conditions for false twistdyeing properties, and torques of the crimped yarns crimping of the drawn yarns using a false twist crimpare shown 1n Table 10. It is seen from this table that ing machine of the type shown in Table 4 in which secaccording to the present invention, even if the temper- 0nd heat-treating devices are arranged at 7, 7 and 8 ature non-uniformity occurs among the spindles, the are given in Table 11.

" i i Table "9 i 7 Sample Q 7 TNT...

Drawing conditions heating means warm water hot roller hot roller hot roller temperature (C) 98 87 85 85 draw ratio (1) 2.40 2.60 2.85 3.4 draw speed (m/min) 600 800 800 800 Physical properties denier Size (dc/01) 168.0/ 1620/30 157.5/30 154.5/30 of the drawn yarn birefringence (A n) 0.068 0.085 0.106 0.124

tenacity at break (g/de) 3.4 3.7 3.8 4,1 elongation at break 96 65 58 density (g/cm") 1.354 1.358 1.360 1.362

False number of false twists (T/M w 2750 2750 2750 2750 False twist draft I2 8 5 3 twist part twist tension at IC.(gr/de) 0.104 0.098 0.099 0.102

crimping heat conditions treating draft l7 l7 l7 l7 part treating temperature (C) 230 230 230 230 processing speed (m/min) I24 124 I24 124 Table T6 Total percentage crimp Dyeing properties Torque of Density of Processing Standard Crimp Standard Dyeing standard standard temperature spindle difi'erence spindle difference spindle spindle (C.) Sample (TCs) (A TC) (Ds) (A D) (T/25 cm) (g/cm Q 13.5 $1 37.3 0.2 11 1.3859 R 12.7 s 1 38.5 0.2 14 1.3860 S 12.3 $1 39.1 0.2 15 1.3858 T 11.0 s 1 39.5 s 0.2 17 1.3862

O 14.4 1 37.5 0.2 14 1.3912 R 14.9 1 38.6 0.2 16 1.3914 S 14.5 s 1 39.0 5 0.2 16 1.3910 T 12.7 I 39.7 50.2 20 1.3911

Q 13.0 2 36.6 0.7 13 1.3954 210 R 13.6 2 37.5 0.7 15 1.3960 S 13.4 5 2 38.2 $0.7 17 1.3957 T 14.3 2 38.5 5 0.7 22 1.3962

Q 9.6 $4 35.1 1.5 10 1.3988 220 R 10.5 54 35.9 $1.5 12 1.3991 S 11.0 4 36.4 51.5 15 1.3989 T 12.1 4 36.7 1.5 20 1.3988

vwfinmmfiflwmm laBT 1T 7min Sample U V heating means hot roller hot roller Drawing conditions temperature (C.) 81

draw ratio (x) 3.70 3.70 draw speed (m/min) 800 800 denier size (dc/til) 156.0/30 144.2/30 Physical properties birefringence (An) 0.162 0.162 of the drawn yarn tenacity at break (g/de) 5.4 5 4 elongation at break 28 28 density (glcm 1.378 1.378

False number of false twists (T/M) 2750 2750 twist part draft 4 -4 False twist twist tension at 190C. (gr/de) 0.368 0.101

crimping heat conditions treating draft 17 -17 Table 1 l-Cohtinued Sample U V part treating temperature (C.) 230 230 processing speed (m/min.) I24 I24 Ten spindles were used for the heat crimping of the drawn yarns, and the processing temperatures were 15;; density (d) ofl.3800 d s 113950 (g/Cm),a

varied from spindle to spindle by a maximum of: 4C. "tdrciutfifim T0535)? based on the standard spindle. Thus, ten false twist 3. A process for producing a false twist-crimped crimped yarns were obtained. The total percentage polyester yarn which comprises false twisting a polyescrimp, dyeing properties and torques of the crimped ter multifilament having a birefringence (An) of 0.030 yarns are shown in Table 12. it is seen from the table An 0.145 while heat setting the filaments in the that in Samples U and V in which the birefringences l5 twisted state at 160 to 210C. atadraft (11,) which satof the drawn yarns are large as in the commercially isfies thefgllowing equation: available conventional drawn yarns of polyester, the 250 An i-38 2 a g 1% -ArT-i-T7i i torque becomes large at the temperatures (above 4. The process of claim 3 wherein the polyester mul- 210C.) at which the yarns have good total percentage tifilament has a birefringence (An) of 0.06 An crimp. Snarl occurs frequently when the crimped yarns g 0.135. are knitted. Furthermore, the dye exhaustion differ- 5. The process of claim 3 wherein the heat setting ence becomes large, and the non-uniformity of dyeing temperature is 170 to 200C. tends to occur among the spindles. 6. A process for producing a modified false twist- Table 12 Total percentage crimp Dyei g P P V 2 2.

Torque of Density of Processing Standard Crimp Standard Dyeing standard standard temperature spindle difference spindle difference spindle spindle (C.) Sample (TCs) (A TC) (Ds) (AD) (T/ cm) (g/cm) 210 U 11.5 $2 43.5 $0.7 23 1.3972 v 14.4 s 2 42.6 s 0.7 27 1.3968

220 U s 4 41.9 s 1.5 27 l.3996 v 9 s4 41.5 $1.5 30 1.4401

What we claim is: i i f crimped polyester yarn which comprises s ubjecting the I. A false twispcrimpm polyester yam havihg a d'enj 40 I false twisti-ctrllmped polyester yarn obtained 1n(;: la1mh3 1;; (d) of 1.3800 s d 2 1.3950 (g/cm 9 total a i i g fi a a l fi a 1 percentage crimp (TC) OfTC g 30 s:rnpera ure a w to e yarn as een tnltta y ea 2. A modified false twist-crlmped polyester yarn hav- 

-250. $N + 38 $ DR $ -150.$N + 17
 2. A modified false twist-crimped polyester yarn having a density (d) of 1.3800 < or = d < or = 1.3950 (g/cm3), a total percentage crimp (TC) of TC < or = 20 (%), and a torque (Tq) of Tq < or = 26 (T/25 cm).
 3. A process for producing a false twist-crimped polyester yarn which comprises false twisting a polyester multifilament having a birefringence ( Delta n) of 0.030 < or = Delta n < or = 0.145 while heat setting the filaments in the twisted state at 160* to 210*C. at a draft (dr) which satisfies the following equation: -250 . Delta n + 38 > or = dr > or = -150. Delta n +
 17. 4. The process of claim 3 wherein the polyester multifilament has a birefringence ( Delta n) of 0.06 < or = Delta n < or = 0.135.
 5. The process of claim 3 wherein the heat setting temperature is 170* to 200*C.
 6. A process for producing a modified false twist-crimped polyester yarn which comprises subjecting the false twist-crimped polyester yarn obtained in claim 3 to a second heat setting at a temperature exceeding the temperature at which the yarn has been initially heat set. 